The invention relates to a method for controlling the cut register in a web-fed rotary press and a computer program for cut register control.
DE 199 36 291 A1 describes a method for determining the positions of cuts of part webs of a longitudinally cut printing material web in a web-fed rotary press, in which the part webs are combined into strands, these are each folded on a former and are finally crosscut by a knife cylinder. In a departure from the aforementioned document, here the cut individual web halves are designated part webs and the cut webs combined after the former are designated strands. The positions of the cuts determined are used to control the cut register, a dedicated control loop being provided for each part web and, in addition, an outer control loop for the already folded strand. The intention is to make it possible to keep the positions of the cuts of all the part webs of each folded strand at a desired value in each case.
Such a control system with a cascade structure is complicated and in particular requires a large number of sensors to register the actual values of the positions of the cut on the individual part webs and also on each folded strand. This is not only costly but as the number of sensors used rises, the probability of failure of the cut register control also increases, since failures of automated systems are generally caused to a predominant extent by sensor failures.
Furthermore, the position of the cut after the folding can be registered with conventional optical means only by using a mark on the respective outer part web of each strand. A displacement of the position of the cut of the inner part webs between the folding former and the knife cylinder can no longer be measured, for which reason the aforesaid cascade control system of the position of the cut of a strand is based on the assumption that a displacement of the position of the cut taking place after the folding has the same extent in all part webs of a folded strand.